>From: David Olofson <[EMAIL PROTECTED]>
>To: "daniel sheltraw" <[EMAIL PROTECTED]>, [EMAIL PROTECTED]
>Subject: Re: [rtl] rt display in usec
>Date: Fri, 11 Aug 2000 18:38:39 +0200
>
>Wed, 09 Aug 2000 daniel sheltraw wrote:
> > Hello RTers
> >
> > This is a bit off the RTL and RTAI topic but I have a quetion similar to
> > Patricks regarding RT display. I am willing to accept the course
> > grained timing given by the reciprocol of the refresh rate but I would
> > like to be able to draw the image to screen with hard RT scheduling.
>There
> > exists a register in most cards that "resets" the sequencer.
>
>Standard VGA register? (Long time since I programmed VGA on the hardware
>level...)
>
> > I am not sure what reset means and can find no documentation to tell so.
>I
> > am wondering if anyone knows whether this resets the sequencer so that I
>can
> > start at a well defined spot in the sequencer cycle and therefore
>achieve
> > hard RT scheduling. Of course there may be latencies for the reset which
> > would have to be taken into account.
>
>Any video card registers (except for the one with the blanking bits, in
>case
>you have no VBL IRQ...) would generally be of interest only when dealing
>with
>hardware accelerated rendering. (If you're using mode-X or bitplane [16
>color]
>modes, you're in trouble, though - these modes require register access all
>the
>time, which means you cannot share the card at the hardware level.) AFAIK,
>the
>only effect they could have on any normal card is that ongoing hardware
>accellerated operations could steal some VRAM bandwidth, which of course
>could
>be a problem if high bandwidth is required for the RT operations.
>
>As to standard VGA registers, I only know about the usual bitmap access
>"helper"
>logic and that stuff, and it is indeed slow on some modern cards, but I
>doubt
>it gets much worse than fiddling with ports in general. "Only" the usual
>hundreds of cycles wasted on waitstates...
>
>If you really need h/w acceleration for the RT stuff, the driver has to run
>in
>RT context, and on nearly all non-pro cards you also need to dedicate the
>card
>to the RT task, since consumer video cards in general cannot switch context
>in
>the middle of an operation.
David
Would you please explain what you mean by "context switch" amd how this
applies to RT?
Thanks Daniel
(Pro cards for CAD/CAM, real time 3D animation etc
>can do this kind of task switching, and it seems like the new generation of
>game
>cards are getting there too, as a result of game and pro cards beginning to
>use
>the same chipsets. Lower costs and higher performance for both classes.)
>
>
>David Olofson
> Programmer
> Reologica Instruments AB
> [EMAIL PROTECTED]
>
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